(1) Field of the invention
This invention relates to semiconductor light sources and detectors and particularly to packaging these devices.
A semiconductor light source or detector comprises a semiconductor chip which is coupled for light transfer communication between an optical fibre tail within the package.
(2) Discussion of the prior art
One example of a packaged semiconductor optical transmission device is disclosed in our published British Pat. No. 2124402 in which FIG. 7 of that patent shows in detail how the optical fibre tail end 60 is secured in relation to the semiconductor chip 31 on a mount 30. A modified arrangement is shown in FIG. 8. In both arrangements the chip and the fibre end are secured to the mount 30 which in turn is secured either directly to the base of the casing 10 or via a Peltier thermo-electric heat pump 129.
It is imporant that the optical axis of the semiconductor chip is aligned with the optical axis of the optical fibre tail and that alignment is maintained throughout the working life of the device. Otherwise only a proportion of the light emanating from the chip or the fibre, depending on whether the device is a source or a detector, will be coupled into the fibre or into the chip, respectively. Clearly therefore it is important that the mounting arrangement within the package for the semiconductor chip is such that maximum coupling can be achieved during manufacture and that coupling remains unaltered through out the life of the device.
We have found that despite the precautions taken in the construction and manufacture of the device just described, nevertheless misalignment of the chip with respect to the fibre can still occur through distortion of the package, either mechanical forces on the package or alternatively thermal stresses.
It is an object of the present invention to provide a package in which misalignment is less likely to occur and which is also significantly cheaper to produce.